Apparatus for cleaning exhaust gases of solid particles, design of a unit for neutralizing harmful gaseous emissions and a method for the manufacture of this unit

ABSTRACT

An apparatus for cleaning exhaust gases of solid particles comprises a rotational combustion chamber (1), a swirler (2) and a soot collector (3) separated from one another by a separating cavity (7) and located on the same axis downstream the gas flow. A catalytic unit (4) for neutralizing harmful gaseous emissions is arranged coaxially inside the soot collector (3). The apparatus is provided with an inlet pipe (8) and an outlet pipe (9). The swirler is made in the form of an impeller. The unit (4) for neutralizing harmful gaseous emissions is made in the form of a cylindrical body (5) comprising longitudinal channels (6) with a catalytically active internal layer applied-thereto. The longitudinal channels (6) have a curvilinear closed-type shape in their cross-section and the catalytically active layer has the same thickness over the entire internal surface of the longitudinal channels (6), which thickness is uniform both over the cross-section of the unit (4) and throughout its length. A method for the manufacture of the unit (4) is based upon obtaining a catalytically active layer on the basis of modified alumina on the surface of a carrier. The catalytic layer is applied by a flame spraying to a flat metallic band carrier. Catalytically inactive substances are used as initial material for flame spraying. Longitudinal channels (6) are formed by corrugating the carrier across its length after the catalytically active layer is applied to it. The band is rolled in parallel with the corrugations so that the catalytically active layer is placed inside the channels (6). Air or other mixture containing oxygen is used as a gas to form plasma during spraying.

FIELD OF THE INVENTION

The invention relates to the field of engineering industry and moreparticularly, automotive industry and namely: to exhaust apparatusprovided with means for cleaning exhaust gases of solid particles, forinstance, soot.

STATE OF PRIOR ART

The state of prior art is featured by the following apparatus.Mercedes-Benz apparatus are shown to be used for retaining solidparticles ("Prospects for Saving Energy and Ecological Influence ofInternal Combustion Engines". Express-Information. Issue "EcologicalProblems on Transport" No. 32, 1992, pp. 24-25, FIG. 12). Theseapparatus are made in the form of special filters in which a winding ofceramic filaments or porous walls retain solid particles. Such filtersallow to ensure a substantial vehicle run (up to 100 km) without burningthe particles that have clogged the filter. Subsequently the filter,when clogged up, undergoes regeneration or is thrown away.

An apparatus is known to be used for afterburning of solid particlescontained in exhaust gases of an internal combustion engine (DE, C,3734197, 1989). This apparatus comprises a rotational combustion chamberin which a catalytic afterburning apparatus (filter) is installed toseparate the combustion chamber into a space upstream the filter and aspace downstream the filter. Upstream the combustion chamber an igniteris mounted that is connected thereto through a tangentially locatedhole. The catalytic unit is made of a ceramic monolith with axialthrough-holes. This apparatus of prior art knowledge allows to cleanexhaust gases of solid particles.

A method is known to be used for producing a catalyst for cleaningexhaust gases (JP, B 3-34367, 22.05.91).

According to this method for applying coatings, a liquid composition isobtained from an activated alumina powder, cerium, powdered. ceria, andzirconium. The composition thus obtained is applied to the surface of amonolith base of carrier, whereupon a catalytic component of noble metalis applied thereto.

A method is known to be used for producing a catalyst for cleaningexhaust gases (JP, A, 2-17943, 22.01.92). According to this method, asuspension is prepared from a powdered mixture of vanadium oxide andalumina in a predetermined proportion according to prescribedtechnology. Then a carrier is submerged into the suspension thusprepared, whereupon it is dried up and calcinated in order to form anoxide surface layer on it, and after this a catalytically activemetal--platinum, rhodium and/or palladium--is precipitated on thecarrier thus coated.

A method is also known to be used for the manufacture of catalytic unitsfor neutralizing harmful gases (EP, A 0203525 22.05.1986). according tothis method, a catalytic composition containing alumina and ceria isapplied to a monolyth honeycombed carrier by precipitation.

The composition is produced by impregnating a water insoluble ceriumcompound with at least one substance of the group consisting of watersoluble aluminum compounds and alumina hydrates, and by calcinating theimpregnation product followed by applying thereto at least one noblemetal of the group consisting of platinum, palladium and rhodium.

The known methods allow to produce a carrier having a large free surfaceof over 100 m² /g, thus ensuring high catalytic activity of suchcarriers.

DISCLOSURE OF THE INVENTION

The Applicant challenges the problem of creating a cleaning systemswhich, simultaneously with cleaning exhaust gases of solid particles,such as soot, would ensure neutralizing harmful gaseous emissions inorder to improve ecology of the air atmosphere. Also, the neutralizingunit of such a system must, in the process of oxidizing soot particles,produce a reducing gas which neutralizes ecologically harmful nitrogenoxides. Besides, the catalytically active layer of the neutralizing unitmust have high adhesive strength at relatively inexpensive production ofsuch a unit.

This problem is solved owing to that the apparatus for cleaning exhaustgases of solid particles, comprising a rotational combustion chamber anda catalytic unit arranged therein, further comprises a swirler and asoot collector separated from one another by a cylindrical separatingcavity and located on the same axis downstream the gas flow, and acatalytic unit for neutralizing harmful gaseous emissions is arrangedcoaxially inside the soot collector. The swirler is made in the form ofan impeller with an angle of incidence within 25 to 55 degrees.

The problem thus posed is also solved owing to that the unit forneutralizing harmful gaseous emissions for the apparatus for cleaningexhaust gases of solid particles is made in the form of a cylindricalbody comprising longitudinal channels with a catalytically activeinternal layer applied thereto. The longitudinal channels have therewithalso a cirvilinear closed-type shape in their sross-section, and thecatalytically active layer has the same thickness over the entireinternal surface of the longitudinal channels, which thickness isuniform both over the cross-section of the unit and throughout thelength thereof.

The problem thus posed is also solved by a method for the manufacture ofthe unit for neutralizing harmful gaseous emissions, in which on thecarrier surface a catalytically active layer is obtained on the basis ofmodified alumina, said catalytically active layer being applied by flamespraying to a flat metallic band carrier. Catalytically inactivesubstances are used as initial material for flame spraying. Then,longitudinal channels are formed by corrugating the flat band carrieracross its length, the carrier is rolled in parallel with itscorrugations while placing a catalytically active layer inside thechannels. Air or other mixture containing oxygen is used as a gas toform plasma during spraying.

The positive effect consists in that the invention allows not onlyseparate solid particles (for instance, those of soot), precipitatingsome of them (that are of large size) and afterburning automatically thesmaller particles in the catalytic unit, but also carry out theafterburning (oxidation) of soot particles to an intermediate stage:producing carbon monoxide which is an efficient reducing agent fornitrogen oxides, and this allows in the final analysis not only to cleanexhaust gases of solid particles, but also to neutralize harmful gaseousemissions.

The invention allows also not only to ensure that the chemical processesof neutralizing harmful gaseous emissions proceed most completely, asenabled also by catalytic units manufactured using familiar methods, butalso to manufacture such a unit that features a high adhesive strengthof its catalytic layer in a streamlined and, hence, inexpensiveproduction procedure.

Actually, flame spraying of a catalytically active layer allows toensure interdiffusion of the carrier material under unbalancedconditions into alumina so that, as a result, there is an increase inthe adhesive strength of the carrier thus produced, when it is used inengines at a temperature of up to 900° C., as well as under conditionsof impacts, thermal shocks, vibration, intensive gas erosion andcorrosion. In addition to this, owing to a high-rate forced applicationof the catalytic layer to the basic carrier--a factor which alsocontributes to an increase in the adhesive strength--it is ensured thata uniform coating both in its chemical composition at its thickness isthus produced, whereas if familiar methods are used, the catalytic layeris deposited on the surface of the carrier unevenly as far as itsthickness and chemical composition are concerned. Together with this, inthe familiar methods it is very difficult to obtain a layer of arequired thickness: impregnation of the carrier by submersion or in asolution, its drying, then again submersion and so on, up to 20-30repeated operations, which is not a good manufacturing practice sincethis leads to a higher labor content and, hence, to making the processtoo expensive. Production of a catalytically active composition on thebasis of thermodynamically unbalanced alumina of γ-modification from acatalytically inactive composition, according to the invention, in aplasma jet allows to improve activity of the catalytic layer due to thefact that the active composition is formed under unbalanced conditionsin the immediate vicinity of the carrier.

The method now claimed also does not require the use of metalliccarriers with a high content of aluminum in a solid solution (up to 5%),which (the carriers) are not suitable for streamlined production and,hence, are expensive. In addition to this, the method now claimed doesnot require to carry out complicated technological operations connectedwith adding insoluble components, such as vanadium oxide, ceria, etc.,to the carrier composition, as usually is made in order to improvecatalytic activity, thermal stability and resistance to poisoning ofcatalysts. In the method now claimed, these components can be readilyadded in the form of thermally decomposable compounds to a catalyticallyinactive composition.

The invention now claimed allows to corrugate a coated band with a verysmall curvature radius, and this also allows to improve catalyticactivity, whereas the prior art methods for applying a catalytic layerby deposition do not allow to apply a layer without a risk of cloggingthe longitudinal channels of the unit.

BRIEF DESCRIPTION OF THE DRAWING

The claimed invention will now be described in more detail withreference to the accompanying drawing which shows schematically theapparatus now claimed (in a longitudinal section view).

THE BEST EMBODIMENT OF THE INVENTION

The apparatus can be realized in the following manner. The apparatuscomprises a rotational combustion chamber 1 inside which in itscylindrical portion a swirler 2 is disposed that is made in the form ofan impeller with an angle of incidence of 45 degrees. In the outletportion of the combustion chamber 1 a soot collector 3 is disposedinside which a catalytic unit 4 for neutralizing harmful emissions iscoaxially arranged. The catalytic unit 4 is essentially a metallic bodyinside which longitudinal channels 6 are made to extend therethrough. Acatalytic ceramic layer is applied to the surfaces of the channels 6.Between the swirler 2 and the soot collector 3 there is a cylindricalseparating cavity 7. The combustion chamber 1 is provided with an inletpipe 8 and an outlet pipe 9. The soot collector 3 is made of alloyedsteel and "hard waste" of thin metallic wire. The unit 4 is made ofhigh-temperature steel. The channels 6 of the unit 4 have a diameter of1.5 to 2.0 mm their length is 90 mm, the ceramic catalytic layer of thecoating is 20 to to 30 microns thick, and the free surface of thecatalytic layer amounts to 50-60 m² /g.

The composition of the coating in percent by weight is as follows:copper oxide--3%, chromium oxide--2%, nickel oxide--1%, cobaltoxide--0.5%, total content of rare-earth metal oxides--1.5% thebalance--alumina of gamma modification.

The apparatus with the unit 4 operates as follows. The effluent gasloaded with solid particles of soot flows to the rotational combustionchamber 1 through the inlet pipe 8 and, while passing through theswirler 2, gets swirled. In the cylindrical separating cavity 7 thesolid particles are separated by weight. Heavier (larger) particlesenter the peripheral region of the cavity 7, then they are trapped bythe soot collector 3 and fall doom to its bottom portion, wherefrom theyare periodically removed in mechanical way. Smaller particles enter thecatalytic unit 4 for neutralizing harmful gaseous emissions. There, theparticles pass through the longitudinal channels 6 extendingtherethrough and come in contact with the catalytic ceramic layer. Asthis takes place, carbon of the soot particles is oxidized to carbonmonoxide, and this is ensured, on one hand, by the chemical and phasecomposition of the catalytic layer and on the other hand by that thechannels 6 are long enough. The gases cleaned of solid particles areemitted through the outlet pipe 9.

Experimentally, it has been found out that making the swirler 2 to havean angle of incidence within the range of 25 to 55 degrees ensures anoptimum fractional separation of the soot particles so that thecatalytic unit 4 for neutralizing gaseous emissions receives theparticles of only that size at which the oxidation of carbon to carbonmonoxide takes place on the catalytic layer of the channels 6.

The apparatus now claimed was tested. A diesel engine was used as asource of effluent gases. As a result, it has been found out that sootparticles and carbon monoxide are completely absent from exhaust gasesafter they pass the apparatus (in the outlet pipe 9), whereas theconcentration of nitrogen oxides reduces from 40 g/kW-hr to 8 g/kW-hr.

The method now claimed can be realized, for instance, as follows. Flamespraying of a catalytically active layer has been carried out in themanufacture of catalytic units for outfitting the neutralizing systemfor harmful gaseous emissions from a "Tavria" car.

Spraying has been carried out in the open air with the use of plasmagenerator (Petrov G. K. "Properties and Characteristics ofWear-Resistant Sprayed and Heat-Treated Air-Plasma Coatings" in thebook: "Gas Thermal Spraying in Industry", Saint-Petersburg, 1993, pp.92-94). Used as a metal carrier has been foil of heat-resistantchromium-aluminum steel with the following parameters: width--90 mm, andthickness--about 40 microns. A piece of band about 5 m long has beenwound in spiral around a steel drum having a diameter of 300 mm andsecured to it, then spraying has been been carried out with the drumbeing simultaneously rotated at a speed of 60 rpm, while a carriage hasbeen moved together with the plasma generator mounted on it long thedrum axis at a rate of 180 mm/min.

The method has been also tried with the following initial composition:

aluminum--8%, aluminum hydroxide: gibbsite--33%, bemite--52%, canadiumcarbonate--2%, chromous carbonate--2%, nickel carbonate--1%, cobaltcarbonate--0.5%, cerium carbonate 0.5%, lanthanum carbonate--0.5%,yttrium carbonate--0.5%.

Spraying conditions: voltage 220V, current 160 A plasma-forming gas(air) feed rate 3 m/s.

As a result of carrying out the spraying process, a catalytic coatinghas been made that has a thickness of 20 microns and the followingchemical composition:

alumina of γ-modification--about 92%

total of vanadium, chromous, nickel, cobalt, cerium, yttrium andlanthanum oxides--about 8%.

After spraying, the metallic band with the catalytic coating has beencorrugated across the band length so that the bending radius is 1.2 mm,and the units have been rolled of them in parallel with the corrugationswith the catalytically active layer facing inside the channels. Thediameter of these units is 40 mm.

INDUSTRIAL APPLICABILITY

The invention may find application in automotive industry when designinginternal combustion engines, including diesel engines, and namely: insystems for neutralizing harmful components of gaseous emissions. Anapparatus with a neutralizing unit is advisable also to be used inmodernizing an exhaust system of automotive vehicles. It can be built-inbetween the engine and the silencer. In this case, the apparatus nowclaimed can perform the functions of the silencer.

The apparatus now claimed was tested. A diesel engine was used as asource of effluent gases. As a result, it has been found out that sootparticles and carbon monoxide are completely absent from exhaust gasesafter they pass the apparatus (in the outlet pipe 9), whereas theconcentration of nitrogen oxides reduces from 40 g/kW-hr to 8 g/kW-hr.

The method now claimed can be realized, for instance, as follows Flamespraying of a catalytically active layer has been carried out in themanufacture of catalytic units for outfitting the neutralizing systemfor harmful gaseous emissions from a "Tavria" car.

Spraying has been carried out in the open air with the use of a plasmagenerator (Petrov G. K. "Properties and Characteristics: ofWear-Resistant Sprayed and Heat-Treated Air-Plasma Coatings" in thebook: "Gas Thermal Spraying in Industry", Saint-Petersburg, 1993 pp.92-94). Used as a metal carrier has been foil of heat-resistantchromium-aluminum steel with the following parameters: width--90 mm, andthickness--about 40 microns. A piece of band about 5 m long has beenwound in spiral around a steel drum having a diameter of 300 mm andsecured thereto then spraying has been carried out with the drum beingsimultaneously rotated at a speed of 60 rpm, while a carriage has beenmoved together with the plasma generator mounted on it along the drumaxis at a rate of 180 mm/min.

The method has been tried with the following initial compositions:

Example 1.

aluminum--8%, aluminum hydroxide: gibbsite--33%, bemite--52%; vanadiumcarbonate--2% chromous carbonate--2% nickel carbonate 1%, cobaltcarbonate--0.5%, cerium carbonate--0.5%, lanthanum carbonate--0.5%,yttrium carbonate--0.5%.

Example 2.

aluminum--5%, aluminum hydroxide (gibbsite)--90%, vanadiumcarbonate--1%, nickel carbonate--0.5%, nickel carbonate--0.5%, tungstencarbonate--0.5%, chromous carbonate--2.0%, lanthanum carbonate--0.5%,yttrium carbonate--0.5%.

Example 3.

Aluminum--3.0%, aluminum hydroxide (bemite)--90%, molybdenumcarbonate--1.0%, cobalt carbonate--0.5%, tungsten carbonate--2.0%,vanadium carbonate--0.5%, chromous carbonate--2.0%, ceriumcarbonate--0.5%, yttrium carbonate--0.5%.

Example 4.

aluminum--8.0%, aluminum hydroxide (gibbsite--60%, bemite--25%)--85%,manganese carbonate--2.0%, ferrous carbonate--2.0%, chromouscarbonate--1.0%, vanadium carbonate--1.0%, cerium carbonate--0.5%,yttrium carbonate--0.5%.

Spraying conditions: voltage 220V, current 160 A, plasma-forming gas(air) flow rate 3 m/s. The catalytic activity increases substantiallywith complex introduction of carbonates, and it is their total ratio toall other components that is of critical importance. Incidentally, inthe above-mentioned group per se there can be any ratio of components,i.e., the proportion in which the carbonates of vanadium, chromium,manganese, iron, cobalt, nickel, niobium, molybdenum, etc., oflanthanoid and yttrium is not subject to strict limitation.

We claim:
 1. An apparatus for cleaning exhaust gases of solid particles,said apparatus comprising a rotational combustion chamber with acatalytic unit arranged therein, said apparatus further comprising aswirler and a soot collector separated from one another by a cylindricalseparating cavity and located on the same axis downstream the gas flow,and the catalytic unit for neutralizing harmful gaseous emissions isarranged coaxially inside the soot collector wherein the swirler is madein the form of an impeller with an angle of incidence within 25 to 55degrees.
 2. The apparatus according to claim 1, Wherein said catalyticunit is made in the form of a cylindrical body comprising longitudinalchannels with a catalytically active internal layer, characterized inthat said longitudinal channels are enclosed and are defined bycurvilinear boundaries in the cross-section thereof, and thecatalytically active layer has the same thickness over the entireinternal surface of said longitudinal channels, which thickness isuniform both over the cross-section of the unit and throughout thelength thereof.
 3. The catalytic unit according to claim 2, wherein saidcatalytic unit is manufactured by a method comprising in obtaining acatalytically active layer on a carrier surface, said layer comprisingbasically of modified alumina, characterized in that said catalyticallyactive layer is applied by flame spraying to a flat metallic bandcarrier, wherein catalytically inactive substances are used as initialmaterial for flame spraying, then longitudinal channels are formed bycorrugating the flat band carriers across the length thereof, thecarrier is rolled in parallel with the corrugations thereof whileplacing said catalytically active layer inside the channels, whereas airor other mixture containing oxygen is used as a gas to form a plasmaduring spraying.